The invention relates to an apparatus at a carding machine having a cylinder, carding elements and displaceable holding elements, which determine the carding spacing between the cylinder clothing and the clothings of the carding elements.
The effective spacing of the tips of a clothing from a machine element lying opposite to the clothing is called the carding gap. The last-mentioned element may also have a clothing but could, instead of that, be formed by a segment of a circuit having a conductive face. The carding gap determines the carding quality. The size (width) of the carding gap is an important machine parameter that shapes both the technology (fibre processing) and the running behaviour of the machine. The carding gap is set as narrow as possible (it is measured in tenths of a millimetre) without the risk of a “collision” of the working elements being incurred. In order to ensure uniform processing of the fibres, the gap needs to be as identical as possible over the whole of the working width of the machine.
The carding gap is affected especially by the machine settings on the one hand and by the condition of the clothing on the other hand. The most important carding gap of the revolving card top carding machine is located in the main carding zone, that is to say between the cylinder and the revolving card top assembly. At least one clothing, which limits the working spacing, is in motion, usually both. In order to increase the production rate of the carding machine, it is sought to select an operating rotational speed, or an operating speed of the moving parts, that is as high as the fibre processing technology allows. The working spacing changes in dependence on the operating conditions. The change occurs in the radial direction (starting from the rotational axis) of the cylinder. The carding gap changes during operation especially as a result of thermal expansion and centrifugal force expansion of the cylinder.
During carding, increasingly large amounts of fibre material are processed per unit of time, which requires higher working component speeds and higher installed outputs. The increasing throughput of fibre material (production rate), even when the working surface area remains constant, results in increased generation of heat as a result of the mechanical work. At the same time, however, the technological carding result (sliver uniformity, degree of cleaning, nep reduction etc.) is constantly being improved, which requires a greater number of effective surfaces in carding engagement and narrower settings of those effective surfaces with respect to the cylinder (tambour). The proportion of synthetic fibres being processed, which—compared with cotton—generate more heat as a result of friction when in contact with the effective surfaces of the machine, is continually increasing. The working components of high-performance carding machines are nowadays totally enclosed on all sides in order to conform to the high safety standards, to prevent the emission of particles into the spinning room environment and to minimise the need for servicing of the machines. Grids or even open, material-guiding surfaces allowing exchange of air are a thing of the past. The said circumstances markedly increase the input of heat into the machine, while the discharge of heat by means of convection is markedly reduced. The resulting more intense heating of high-performance carding machines leads to greater thermoelastic deformation which, on account of the non-uniform distribution of the temperature field, affects the set spacings of the effective surfaces: the gaps between cylinder and card top, doffer, fixed card tops and take-off stations with blades are reduced. In an extreme case, the set gap between the effective surfaces can be completely consumed by thermal expansion, so that components moving relative to one another collide, resulting in considerable damage to the affected high-performance carding machine. Accordingly, particularly the generation of heat in the working region of the carding machine can lead to different degrees of thermal expansion when the temperature differences between the components are too great.
In order to reduce or avoid the risk of collisions, the carding gap between clothings lying opposite to one another is in practice set relatively wide, that is to say a certain safety spacing exists, but a large carding gap results in undesired nep formation in the card sliver. On the other hand, an optimum, especially narrow, dimension, by means of which the proportion of nep in the card sliver is appreciably reduced, is desirable.
In a known apparatus (DE 29 48 825 C), a displacement device actuatable by thermal energy supply is provided for compensating for changes in the carding spacing that arise during operation, at least one adjusting element, for example a rod, cooperating with a fluid, for example oil, and the thermal energy being conveyable to the fluid. For the purpose of effecting the supply of heat by means of a fluid, a protective cover is connected to a fluid supply line and to a fluid discharge line, which open into a container for the fluid. Installed in the fluid supply line is a pump by means of which the fluid can be fed under pressure from the container into the chamber formed round the metal rod by the protective cover. Using a heating device (for example an electrical resistance heating device), the fluid is so heated in the container, to a particular temperature determined by a control means, that the rod is able to expand to a greater or lesser degree. The adjusting devices may comprise a liquid (water, oil) or a gas (for example air), and can effect positioning of the guide bend (flexible bend) on which the ends of the clothed flats slide. In that apparatus, heat thus acts on the liquid, the liquid transfers the heat to a stationary metal rod and the metal rod rotates as a result, the position of the flats, and hence the carding space, being changed by way of the guide bends. A disadvantage is that the heating of metals, both ferrous and non-ferrous, reduces the modulus of elasticity, for example by 20%. Given that the adjusting element is in a resiliently pre-biased state on account of the pre-biasing of the guide bend, additionally compensation for that difference is required, which is of considerable expense in terms of apparatus. A further problem is that a metal rod of a particular length, for example 150 mm, requires a high energy supply, for example heating by about 300°K, to achieve an expansion of, for example, 0.3 mm.
It is an aim of the invention to provide an apparatus of the type described at the outset that avoids or mitigates the mentioned disadvantages and that especially makes it possible, in a structurally simple manner, to keep the carding gap constant or substantially constant.